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Health Risk of grinding trivalent chromated parts?

I run a Sheet Metal shop in Oregon and have a question about the safety of Sanding parts after they have been through the Trivalent Chromate process. I have some parts that require a Trivalent Chromate and then get a Powder Coat finish applied. We often times need to sand the parts before Powder Coating to remove scratches. I'm wondering how toxic is the dust that's created during this sanding prep?

Dan P
Sheet Metal Manager - Hillsboro, OR, USA
2007

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I doubt that the tiny amount of trivalent chromium contributes much to toxicity; it's even used as a vitamin supplement by health store types.

But how toxic is glass? It's probably the least toxic construction material in history, but glass dust is terrible for your lungs and inhaling shards will likely kill you. The point being, no grinding dust should ever be inhaled, then you don't have to worry about the trivalent chromate. Only an opinion -- everybody's got one.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

So in your opinion would you say that the use of a good down draft table and a dust mask would be sufficient protection during the sanding process? Thanks for the consultation on this subject.

Dan P
- Hillsboro, OR, USA
2007

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In my estimation, yes, Dan. But I would not challenge anyone who feels otherwise because my expertise is more in wet process metal finishing than mechanical prep and dust capture.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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What if instead of applying the chromate after the zinc plating, you applied a light zinc phosphate coating? Then, you simply eliminate the sanding, which is taking off what protection the trivalent dip provides, anyway.

Dave Wichern
Consultant - The Bronx, New York
2007

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I don't think we've yet established whether the metal is zinc plated steel or whether it's aluminum, David. But you raise a good point that pretreatment doesn't do much good if you're going to sand it off :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007

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The material is 5052 aluminum and it is just chromated (Alodine T 5900) before the Powder Coat process. Were just removing any scratching that occurred between the finish process and Powder Coat process that may show through the final Powder finish. The chromate is basically just a cleaning prep process for the Powder Coat. It also provides corrosion resistance for any masked surfaces (if not sanded).

Dan P
- Hillsboro, OR, USA
2007

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I must admit I did nor read your original post very carefully - I figured the purpose of the sanding was to promote better adhesion of the powder coating.

Why not sand, then chromate?

Dave Wichern
Consultant - The Bronx, New York
2007

Or why not Powder Coat, then sand? :)

Dan P
- Hillsboro, OR, USA
2007

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Dan, I think a point that Dave was making was that the chromate is not just for cleaning and not just for the areas that are not powder coated, but that pretreatment is an important part of the powder coating process. Good luck.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2007